Diagnostics and modeling of a hollow-cathode arc deposition plasma

Abstract

Methane or acetylene added to an argon or helium arc plasma is dissociated and/or ionized effectively in order to deposit amorphous carbon (a-C:H) layers. The plasma can be confined or spread out by a homogeneous or cusp magnetic field. The issue of the present study is whether the magnetic confinement has an influence on the type of ions governing the deposition and their energy. To this end, an energy-resolved mass spectrometer (plasma monitor) was used, screened off by a μ-metal cage. It appears that, for strong magnetic fields of up to 10 mT, besides CH3+ and C2H2+ ions (from the methane and acetylene admixture, respectively), also relatively more dissociated species like CHx+ (x=2, 1, 0) and CyHz (y=2, 1, 0; z=1, 0) arise. Especially with the C2H2 admixture, atomic C+ ions appear to become more abundant with increasing magnetic field. The energy of the ions appears to decrease with increasing magnetic field. With Langmuir cylindrical electric-probe measurements it was confirmed that this is related to a decreasing plasma potential. By means of a numerical model, spatially resolved density profiles of the most important species were calculated. Depending on the reactor parameters, relevant ion densities are of the order of 109–1010 cm−3, resulting in deposition rates of up to some μm h−1.